Semiconductor wafers are subjected to numerous steps during processing. This usually entails transporting a plurality of wafers between workstations or facilities for processing. Semiconductor wafers are delicate and easily damaged by physical contact or shock and by static electricity. Further semiconductor manufacturing processes are extremely sensitive to contamination by particulates or chemical substances. Consequently, in order to reduce the deleterious effect of contaminants on wafers, specialized containers have been developed to minimize the generation of contaminants and to isolate wafers from contaminants exterior to the containers. These containers typically include a removable door with gasketing or other means for providing a tight seal of the door with the container body.
As semiconductors have become smaller in scale, that is, as the number of circuits per unit area has increased, contaminants in the form of particulates have become more of an issue than previously. The size of particulates that can destroy a circuit has decreased and is approaching the molecular level. Consequently, ever better particulate control is desirable during all phases of manufacturing, processing, transporting, and storage of semiconductor wafers.
Wafer carriers are typically made from thermoplastic materials. Early containers, for example the container disclosed in U.S. Pat. No. 4,248,346, were made of highly moldable plastics such as polyethelene. Later containers, such as disclosed in U.S. Pat. No. 5,273,159, held rigid h-bar carriers, and are often made from polycarbonate with molded in slots and with softer, more resilient, covers such as disclosed in U.S. Pat. No. 5,586,658 for example. Each of U.S. Pat. Nos. 4,248,346; 5,273,159; and 5,586,658 are hereby fully incorporated herein by reference.
Some of the prior containers have a door to enclosure portion seal and also have the capability to sealingly engage to process equipment. Such containers have been termed “SMIF pods” (Standard Mechanical Interface) where the door closes an open bottom of the container portion, or FOUPs (Front Opening Unified Pods) and FOSBs (Front Opening Shipping Box) where the door closes an open front. These containers are subjected to very demanding structural requirements and performance requirements. For example, they must be mechanically sealably latchable by both robotic and manual means and must be hermetically sealable simply by closing and latching the door in place on the container.
Conventional seals for both SMIF pods and transport modules have typically been relatively simple elastomeric seals that are simply compressed between the door and enclosure portion in an axial direction to provide the seal. Such seals, particularly where polycarbonate material is contacted by the elastomeric seal, tend to stick excessively and provide inconsistent opening, reduced life expectancy of the seal and inadequate sealing.
More recent designs have featured seal cross-sections that feature a bridging portion that extends radially outward to a perpendicular distal portion, and provide a seal by knife edge contact with the bridging portion as well as axial compression of the distal portion. An example of such a design is found in U.S. patent application Ser. No. 09/998,621 entitled “SEALING ELEMENT, HERMETIC CONTAINER AND SEALING METHOD THEREOF” by Takahashi, et. al., hereby fully incorporated herein by reference. A problem with this approach, however, is “divergent column buckling” of the distal portion, wherein the free end of the distal portion buckles radially inward throughout one tangential segment of the seal, but buckles radially outward at a different tangential segment. Such a scenario allows for the seal to leak at the transition point between the inward and outward buckling.
What is needed in the industry is a better performing and longer lasting seal structure for sealing a door with the enclosure of a wafer container.